Process for preparing raw materials for washing agents

ABSTRACT

A process for producing solid detergent granular materials is presented involving (a) forming an aqueous surfactant paste of an anionic surfactant, an amphoteric surfactant or mixtures thereof, and (b) drying and granulating the aqueous paste in a horizontal thin-layer evaporator or dryer having rotating fittings, wherein the drying is carried out at a temperature of 120° C. to 130° C. The process produces granules having a bulk density greater than 600 grams/liter and a uniform particle size distribution.

This application is filed under 35 U.S.C. 371 and based onPCT/EP98/00891, filed Feb. 17, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the contact drying of aqueoussurfactant pastes in a horizontal thin-layer evaporator or dryer.

2. Discussion of Related Art

Anionic and amphoteric or zwitterionic surfactants are importantingredients of solid detergents and bar soaps. The detergents arenormally produced by spraying an aqueous, generally highly alkalineslurry of the ingredients and drying the slurry with hot inert gasesflowing in countercurrent. However, since this conventional spray dryingprocess is accompanied by serious pollution of the waste air withorganic material, there is a need for alternative, ecologically morefavorable drying processes. These include in particular the contactdrying of water-containing surfactant pastes in thin-layer dryers whichleads to dry products which can then be processed with the other drieddetergent ingredients, for example in mixers, to form the end product.

European patent application EP-A1 0 572 957 (Kao) describes a processfor drying alkyl or alkyl ether sulfates in which dilute surfactantpastes are first concentrated to an active substance content of 60 to80% by weight and are then dried in vacuo at temperatures of 50 to 140°C. in a vertical thin-layer evaporator. However, a major disadvantage ofthis process is that, because drying is carried out under reducedpressure, the end product has to be removed from the circuit usingcomplicated equipment suitable for operation in a vacuum. The continuouscontact with the hot product means that there is always a danger ofcaking and, hence, operational disturbances which necessitate a completestoppage of production so that cleaning can be carried out. Anothermajor disadvantage is that the use of a vertical thin-layer evaporatorwith wall contact of the rotor blades means that a flowable product filmhas to be maintained on the wall of the evaporator over its entirelength in continuous operation in order to avoid mechanical overloadingof the evaporator. Accordingly, the process is not suitable for thedirect production of a powder, but only for the production of aconcentrated hotmelt which has to be separately crystallized (forexample in a flaking roller or the like) and then size-reduced.

By contrast, International patent application WO 96/06916 (Unilever)proposes a process for drying water-containing anionic surfactant pastesin a horizontal thin-layer evaporator which operates under a lightvacuum to almost normal pressure and at temperatures above 130° C.Another feature of this process is the use of a very high peripheralspeed of the stirrers used of at least 15 m/s which virtually rules outdirect wall contact and leads to products of satisfactory color.However, in the drying of water-containing anionic surfactant pastes,more particularly aqueous pastes of alkyl sulfates or alkyl ethersulfates, there is basically a risk of unwanted hydrolysis in theproduct. Even brief reduction of the pH value leads in the presence ofwater to rehydrolysis, to the formation of inorganic sulfate and to areduction in the content of washing-active substance. In following theteaching of WO 96/06916, applicants found that a hydrolysis-free productcould not be reproducibly obtained over an operating period of severalhours.

Accordingly, the complex problem addressed by the present invention wasto provide a process for the contact drying of water-containing anionicsurfactant and/or amphoteric surfactant pastes which would not have anyof the disadvantages mentioned above and which, despite minimal outlayon equipment, would lead under production conditions to hydrolysis-free,free-flowing granules of satisfactory color distinguished by high bulkdensities and a uniform particle size distribution.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the production of soliddetergent raw materials by simultaneously drying and granulatingwater-containing pastes of anionic and/or amphoteric surfactants in ahorizontal thin-layer evaporator or dryer with rotating fittings,characterized in that drying is carried at a temperature in the rangefrom 120 to 130° C.

It has surprisingly been found that free-flowing granules ofsatisfactory color can be obtained only and precisely when the dryingtemperature is kept in the range mentioned. Even minor upward deviationslead to an unwanted increase in the content of inorganic sulfate whileslight downward deviations lead to products with unsatisfactory flowproperties. The invention includes the observation that the tendencytowards hydrolysis can be further suppressed by carrying out the contactdrying process in the presence of (a) 0.05 to 0.5% by weight of alkalimetal carbonate and/or (b) an alkaline gas stream. The water is removedpreferably by a gas stream and not by applying a vacuum. Anotheradvantage of the process according to the invention is that it givesproducts of high bulk density (above 600 g/l) which, irrespective of thesurfactant paste used, have a very uniform particle size distribution.

Surfactants

Typical examples of anionic surfactants which can be dried by theprocess according to the invention are soaps, alkyl benzenesulfonates,alkane sulfonates, olefin sulfonates, alkyl ether sulfonates, glycerolether sulfonates, α-methyl ester sulfonates, sulfofatty acids, alkylsulfates, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxymixed ether sulfates, monoglyceride (ether) sulfates, fatty acid amide(ether) sulfates, mono- and dialkyl sulfosuccinates, mono- and dialkylsulfosuccinamates, sulfotriglycerides, amide soaps, ether carboxylicacids and salts thereof, fatty acid isethionates, fatty acidsarcosinates, fatty acid taurides, N-acyl amino acids such as, forexample, acyl lactylates, acyl tartrates, acyl glutamates and acylaspartates, alkyl oligoglucoside sulfates, protein fatty acidcondensates (more particularly vegetable wheat-based products), alkyl(ether)phosphates and sulfates of ring-opening products of olefinepoxides with water or alcohols. Where the anionic surfactants containpolyglycol ether chains, they may have a conventional homologdistribution although they preferably have a narrow homologdistribution. Typical examples of amphoteric or zwitterionic surfactantsare alkyl betaines, alkyl amidobetaines, aminopropionates,aminoglycinates, imidazolinium betaines and sulfobetaines. Thesurfactants mentioned are all known compounds. Information on theirstructure and production can be found in relevant synoptic works, cf.for example J. Falbe (ed.), “Surfactants in Consumer products”, SpringerVeriag, Berlin, 1987, pp. 54-124 or J. Falbe (ed.), “Katalysatoren,Tenside und Mineralöladditive”, Thieme Verlag, Stuftgart, 1978, pp.123-217.

In the context of the invention, water-containing pastes are understoodto be aqueous preparations of the surfactants which have an activesubstance content of 5 to 80% by weight and preferably 10 to 70% byweight. For energy-related and rheological reasons, it is of advantageto use pastes which have a solids content of at least 30% by weight andpreferably 50% by weight and at most 70% by weight. The anionicsurfactants are used in the form of their alkali metal, alkaline earthmetal, ammonium, alkylammonium, alkanolammonium, glucammonium salts. Inother preferred embodiments of the process, alkyl and/or alkenyl(ether)sulfates, sulfosuccinates and/or betaines are dried and processedto light-colored, free-flowing granules.

Alkyl and/or Alkenyl Sulfates

In the context of the invention, alkyl and/or alkenyl sulfates, whichare also often referred to as fatty alcohol sulfates, are understood tobe the sulfation products of primary alcohols which correspond toformula (I):

R¹O—SO₃X  (I)

where R¹ is a linear or branched, aliphatic alkyl and/or alkenyl groupcontaining 6 to 22 and preferably 12 to 18 carbon atoms and X is analkali metal and/or alkaline earth metal, ammonium, alkylammonium,alkanolammonium or glucammonium. Typical examples of alkyl sulfateswhich may be used in accordance with the present invention are thesulfation products of caproic alcohol, caprylic alcohol, capric alcohol,2-ethylhexyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol,palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol,elaidyl alcohol, petroselinyl alcohol, arachyl alcohol gadoleyl alcohol,behenyl alcohol and erucyl alcohol and the technical mixtures thereofobtained by the high-pressure hydrogenation of technical methyl esterfractions or aldehydes from Roelen's oxosynthesis. In addition, Guerbetalcohols containing 16 to 32 carbon atoms may also serve as rawmaterials. The sulfation products may advantageously be used in the formof their alkali metal salts, especially their sodium salts. Alkylsulfates based on C_(16/18) tallow fatty alcohols or vegetable fattyalcohols with a comparable C chain distribution in the form of theirsodium salts are particularly preferred.

Alkyl and/or Alkenyl Ether Sulfates

Alkyl and/or alkenyl ether sulfates (“ether sulfates”) are known anionicsurfactants which are industrially produced by SO₃ or chlorosulfonicacid (CSA) sulfation of oxoalcohol or fatty alcohol polyglycol ethersand subsequent neutralization. Ether sulfates suitable for the purposesof the invention correspond to formula (II):

R²O—(CH₂CH₂O)_(m)SO₃X  (II)

where R² is a linear or branched alkyl and/or alkenyl group containing 6to 22 carbon atoms, m is a number of 1 to 10 and X is an alkali and/oralkaline earth metal, ammonium, alkylammonium, alkanolammonium orglucammonium. Typical examples are the sulfates of addition products ofon average 1 to 10 and, more particularly, 2 to 5 moles of ethyleneoxide with caproic alcohol, caprylic alcohol, 2-ethylhexyl alcohol,capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl alcohol,cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol,oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol,gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidyl alcoholand technical mixtures thereof in the form of their sodium and/ormagnesium salts. Adducts of ethylene oxide with Guerbet alcoholscontaining 16 to 32 carbon atoms may also be used as raw materials. Theether sulfates may have both a conventional homolog distribution and anarrow homolog distribution. A particularly preferred embodimentcomprises using ether sulfates based on adducts of on average 2 to 3moles of ethylene oxide with technical C_(12/14) or C_(12/18) cocofattyalcohol fractions in the form of their sodium and/or magnesium salts.

Sulfosuccinates

Sulfosuccinates, which are also referred to as sulfosuccinic acidesters, are known anionic surfactants which may be obtained by therelevant methods of preparative organic chemistry. They correspond toformula (III):

where R³ is an alkyl and/or alkenyl group containing 6 to 22 carbonatoms, R⁴ has the same meaning as R³ or X, p and q independently of oneanother stand for 0 or for numbers of 1 to 10 and X is an alkali metalor alkaline earth metal, ammonium, alkylammonium, alkanolammonium orglucammonium. They are normally produced from maleic acid, butpreferably from maleic anhydride, which in a first step is esterifiedwith optionally ethoxylated primary alcohols. The monoester-to-diesterratio can be adjusted at this stage by varying the quantity of alcoholand the temperature. The second step comprises the addition of bisulfitewhich is normally carried out in methanol as solvent. Fairly recentoverviews of the production and use of sulfosuccinates have beenpublished, for example, by T. Schoenberg in Cosm. Toil. 104, 105 (1989),by J. A. Milne in R. Soc. Chem. (Ind. Appl. Surf. II) 77, 77 (1990) andby W. Hreczurch et al. in J. Am. Oil. Chem. Soc. 70, 707 (1993). Typicalexamples are sulfosuccinic acid monoesters and/or diesters in the formof their sodium salts which are derived from fatty alcohols containing 8to 18 and preferably 8 to 10 or 12 to 14 carbon atoms. The fattyalcohols may be etherified with on average 1 to 10 and preferably 1 to 5moles of ethylene oxide and may have both a conventionaland—preferably—a narrow homolog distribution. Di-n-octyl sulfosuccinateand monolauryl-3EO-sulfosuccinate in the form of their sodium salts arementioned as examples.

Betaines

Betaines are known surfactants which are mainly obtained bycarboxyalkylation, preferably carboxymethylation, of aminic compounds.The starting materials are preferably condensed with halocarboxylicacids or salts thereof, especially sodium chloroacetate, 1 mole of saltbeing formed per mole of betaine. Another suitable method is theaddition of unsaturated carboxylic acids, for example acrylic acid.Information on the nomenclature and above all on the difference betweenbetaines and “true” amphoteric surfactants can be found in the articleby U. Ploog in Seifen-Öle-Fette-Wachse, 198, 373 (1982). Other overviewson this subject have been published, for example, by A. O'Lennick et al.in HAPPI, November 70 (1986), by S. Holzman et al. in Tens. Det. 23, 309(1986), by R. Bibo et al. in Soap Cosm. Chem. Spec. Apr. 46 (1990) andby P. Ellis et al. in Euro Cosm. 1, 14 (1994). Examples of suitablebetaines are the carboxy-alkylation products of secondary and, moreparticularly, tertiary amines corresponding to formula (IV):

in which R⁵ represents alkyl and/or alkenyl groups containing 6 to 22carbon atoms, R⁶ represents hydrogen or alkyl groups containing 1 to 4carbon atoms, R⁷ represents alkyl groups containing 1 to 4 carbon atoms,x is a number of 1 to 6 and Y is an alkali metal and/or alkaline earthmetal or ammonium. Typical examples are the carboxymethylation productsof hexyl methyl amine, hexyl dimethyl amine, octyl dimethyl amine, decyldimethyl amine, dodecyl methyl amine, dodecyl dimethyl amine, dodecylethyl methyl amine, C_(12/14) cocoalkyl dimethyl amine, myristyldimethyl amine, cetyl dimethyl amine, stearyl dimethyl amine, stearylethyl methyl amine, oleyl dimethyl amine, C_(16/18) tallow alkyldimethyl amine, Guerbet amines and technical mixtures thereof.

Also suitable are carboxyalkylation products of amidoamines whichcorrespond to formula (V):

where R⁸CO is an aliphatic acyl group containing 6 to 22 carbon atomsand 0 or 1 to 3 double bonds, y is a number of 1 to 3 and R⁶, R⁷, x andY are as defined above. Typical examples are reaction products of fattyacids containing 6 to 22 carbon atoms, namely caproic acid, caprylicacid, capric acid, lauric acid, myristic acid, palmitic acid,palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidicacid, petroselic acid, linoleic acid, linolenic acid, elaeostearic acid,arachic acid, gadoleic acid, behenic acid, erucic acid, Guerbet acids,and technical mixtures thereof, with N,N-dimethylaminoethyl amine,N,N-dimethylaminopropyl amine, N,N-diethylaminoethyl amine andN,N-diethylaminopropyl amine which are condensed with sodiumchloroacetate. A condensation product of C_(8/18) cocofattyacid-N,N-dimethylaminopropyl amide with sodium chloroacetate ispreferably used.

Other suitable starting materials for the betaines to be used inaccordance with the invention are imidazolines. These substances arealso known substances which may be obtained, for example, by cyclizingcondensation of 1 or 2 moles of fatty acid with polyfunctional amines,for example aminoethyl ethanolamine (AEEA) or diethylenetriamine. Thecorresponding carboxyalkylation products are mixtures of differentopen-chain betaines. Typical examples are condensation products of theabove-mentioned fatty acids with AEEA, preferably imidazolines based onlauric acid or C_(12/14) cocofatty acid which are subsequentlybetainized with sodium chloroacetate.

Alkyl and/or Alkenyl Oligoglycosides

In one particular embodiment of the invention, the anionic or amphotericsurfactants are dried together with nonionic surfactants of the alkyland/or alkenyl oligoglycoside type which correspond to formula (VI):

R⁹O—[G]_(p)  (VI)

where R⁹ is an alkyl and/or alkenyl radical containing 4 to 22 carbonatoms, G is a sugar unit containing 5 or 6 carbon atoms and p is anumber of 1 to 10. They may be obtained by the relevant methods ofpreparative organic chemistry, for example by acid-catalyzedacetalization of glucose with fatty alcohols. The alkyl and/or alkenyloligoglycosides may be derived from aldoses or ketoses containing 5 or 6carbon atoms, preferably glucose. Accordingly, the preferred alkyland/or alkenyl oligoglycosides are alkyl and/or alkenyl oligoglucosides.The index p in general formula (VI) indicates the degree ofoligomerization (DP), i.e. the distribution of mono- andoligoglycosides, and is a number of 1 to 10. Whereas p in a givencompound must always be an integer and, above all, may assume a value of1 to 6, the value p for a certain alkyl oligoglycoside is ananalytically determined calculated quantity which is generally a brokennumber. Alkyl and/or alkenyl oligoglycosides having an average degree ofoligomerization p of 1.1 to 3.0 are preferably used. Alkyl and/oralkenyl oligoglycosides having a degree of oligomerization of less than1.7 and, more particularly, between 1.2 and 1.4 are preferred from theapplicational point of view.

The alkyl or alkenyl radical R⁹ may be derived from primary alcoholscontaining 4 to 11 and preferably 8 to 10 carbon atoms. Typical examplesare butanol, caproic alcohol, caprylic alcohol, capric alcohol andundecyl alcohol and the technical mixtures thereof obtained, forexample, in the hydrogenation of technical fatty acid methyl esters orin the hydrogenation of aldehydes from Roelen's oxosynthesis. Alkyloligoglucosides having a chain length of C₈ to C₁₀ (DP=1 to 3), whichare obtained as first runnings in the separation of technical C₈₋₁₈coconut oil fatty alcohol by distillation and which may contain lessthan 6% by weight of C₁₂ alcohol as an impurity, and also alkyloligoglucosides based on technical C_(9/11) oxoalcohols (DP=1 to 3) arepreferred. In addition, the alkyl or alkenyl radical R⁹ may also bederived from primary alcohols containing 12 to 22 and preferably 12 to14 carbon atoms. Typical examples are lauryl alcohol, myristyl alcohol,cetyl alcohol, palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol,oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, arachyl alcohol,gadoleyl alcohol, behenyl alcohol, erucyl alcohol, brassidyl alcohol andtechnical mixtures thereof which may be obtained as described above.Alkyl oligoglucosides based on hydrogenated C_(12/14) coconut oil fattyalcohol having a DP of 1 to 3 are preferred.

The co-drying process may be carried out by mixing and homogenizing theaqueous pastes of the various surfactants beforehand and thenintroducing the resulting homogenized mixture into the thin-layerevaporator. However, the pastes may also be separately introduced andmixed in situ. The ratio by weight between the anionic/amphotericsurfactants and alkyl and/or alkenyl oligoglycosides can be in the rangefrom 10:90 to 90:10, based on the washing-active substance content, andis preferably in the range from 25:75 to 75:25. Mixtures ofsulfosuccinates and alkyl oligoglucosides in a ratio by weight of 40:60to 60:40 are particularly preferred and, after drying, are eminentlysuitable for the production of bar soaps.

Drying and Granulation in a Flash Dryer

The simultaneous drying and granulation are carried out in ahorizontally arranged thin-layer evaporator or dryer with rotatingfittings of the type marketed, for example, by the VRV Company under thename of “Flashdryer” or by the VOMM Company under the name of“Turbodryer”. In simple terms, these dryers are tubes which can beheated to different temperatures over several zones. The paste-formstarting material which is introduced by a pump is projected by one ormore shafts equipped with blades or plowshares as rotating fittingsagainst the heated wall on which drying takes place in the form of athin layer typically between 1 and 10 mm thick. According to theinvention, it has proved to be of advantage to apply a temperaturegradient from 130 (product entry) to 20° C. (product exit) to thethin-layer evaporator. This can be done, for example, by heating thefirst two zones of the evaporator to 120-130° C. and cooling the lastzone to 20° C. The thin-layer evaporator or dryer is operated atatmospheric pressure. Air, but preferably an alkaline gas stream, forexample ammonia, is passed through in countercurrent (throughput 50 to150 m³/h). The gas entry temperature is generally in the range from 20to 30° C. while the gas exit temperature is in the range from 90 to 110°C. The throughput of the surfactant pastes is of course dependent on thesize of the dryer and amounts, for example, to between 5 and 25 kg/h. Itis advisable to heat the pastes to 40 to 60° C. as they are fed into thedryer and to add alkali metal carbonate, preferably sodium carbonate, tothem in quantities of 0.05 to 0.5% by weight, based on the solidscontent, in order to avoid hydrolysis processes.

Another preferred embodiment of the process according to the inventioncomprises mixing the water-containing surfactant with already dried endproduct on the hot contact surface. To this end, a partial stream of theproduct of about 10 to 40% by weight and preferably 15 to 25% by weight,based on the mass flow of the paste used, is removed at the dryer exitand directly re-introduced into the apparatus in the immediate vicinityof the paste entry point by means of a solids metering screw. It ispossible by applying this measure to reduce the tackiness of thewater-containing surfactant and to establish better wall contact of theproduct over the entire available surface. This makes product transportmore uniform and intensifies drying of the product. At the same time,the particle size distribution of the granules can be shifted undercontrol towards coarser products, i.e. the unwanted fine particlecomponent can be significantly reduced, by the addition of the endproduct. This measure provides for an increase in throughput, based onanalogous process conditions with no recycling of solids.

After drying, it has also proved to be of considerable advantage totransfer the granules, which still have a temperature of about 50 to 70°C., to a conveyor belt, preferably in the form of a vibrating chute orthe like, and rapidly to cool them, i.e. in 20 to 60 seconds, totemperatures of around 30 to 40° C. using ambient air. In order toimprove their resistance to unwanted water absorption, the granules ofparticularly hygroscopic surfactants may also be powdered or dusted withsilica in a quantity of 0.5 to 2% by weight.

COMMERCIAL APPLICATIONS

The granules obtainable by the process according to the invention maysubsequently be mixed with other ingredients of powder-formsurface-active compositions, for example tower powders for detergents.The powders may also readily be incorporated in water-basedpreparations. In fact, there are no differences in performanceproperties between the powders on the one hand and the aqueous startingpastes on the other hand. The granules may readily be incorporated, forexample together with fatty acids, fatty acid salts, fatty alcohols,starch, polyglycols and the like, in bar soaps of the combination bar orsyndet type and toothpastes or may be used for the production ofemulsifiers for emulsion polymerization.

EXAMPLES Examples 1 to 5

The granules were produced in a flash dryer of the type manufactured byVRV S.p.A. of Milan, Italy. This dryer is a horizontally arrangedthin-layer evaporator (length 1100 mm, internal diameter 155 mm) with 4shafts and 22 blades which are arranged at a distance of 2 mm from thewall. The dryer has three separate heating and cooling zones and a totalheat-exchange surface of 0.44 m². It is operated at normal pressure.Water-containing surfactant pastes (solids content 70% by weight)optionally containing 1% by weight of sodium carbonate as additive andheated to 50° C. were pumped by a vibrating pump (throughput 11.5 kg/h)into the thin-layer evaporator in which heating zones 1 and 2 had beenadjusted to 125° C. and cooling zone 3 to a temperature of 20° C. Thespeed of the rotors was 24 m/s. Air or a 1:1 mixture of air and ammoniawas passed through the flash dryer (ca. 110 m³/h). The gas exittemperature was ca. 65° C. The predried granules, which still had atemperature of about 60° C., were transferred to a vibrating chute(length 1 m), exposed to ambient air and cooled in 30 seconds to atemperature of around 40° C. The granules were then dusted/powdered withabout 1% by weight of silica (Sipernat® 50 S). Dry, pure white granuleswere obtained and remained free flowing, i.e. did not form any lumps,even after prolonged storage in air. The characteristic data of thegranules are set out in Table 1.

TABLE 1 Characteristic data of the flash dryer granules (percentages = %by weight) Particle size distribution [%] in Surfactant mm RW BD Ex.paste >0.8 >0.4 >0.2 >0.1 <0.1 [%] [g/l] 1 Sodium Lauryl 11.1 19.0 24.231.0 14.7 1.3 610 Sulfate¹⁾ 2 Sodium 11.8 21.0 26.3 35.5 5.4 1.2 615Laureth Sulfate¹⁾ 3 Sodium 12.0 13.4 27.1 34.0 13.5 1.3 620 LaurethSulfo- succinate²⁾ 4 Cocoamido- 12.2 12.7 23.5 33.7 17.9 1.3 610 propylBetaine 5 Sodium 11.9 12.5 22.9 32.7 20.0 1.3 600 Laureth Sulfo-succinate/ Coco Glucosides (1:1)²⁾ ¹⁾Addition of sodium carbonate to thepaste, air/ammonia gas stream ²⁾Addition of sodium carbonate to thepaste RW = Residual water content of the granules BD = Bulk density

Examples 6 to 11

Alkyl sulfate pastes were dried in the same way as described in Example1 except that a partial product stream (Examples 7, 8 and 11) wasremoved at the dryer exit and directly returned to the dryer in theimmediate vicinity of the paste entry point by means of a solidsmetering screw. The results are set out in Table 2.

TABLE 2 Drying of AS pastes with recycling (percentages = % by weight)Parameter 6 7 8 9 10 11 Starting material 1 1 1 2 2 2 Drying temperature[° C.] 128 Flow rate of paste [kg/h] 8.5 11.5 13.5 8.5 11.3 11.3 Flowrate of solids [kg/h] — 3.5 1.7 — — 1.7 Water content of end product 0.40.4 0.4 0.7 1.3 1.0 [%] Bulk density [g/l] 557 593 654 657 Particle sizedistribution [%] >0.8 mm 11.1 29.4 0.8 0.7 >0.4 mm 19.0 30.2 3.09.1 >0.2 mm 24.2 23.9 7.2 19.7 >0.1 mm 31.0 13.1 32.2 45.7 <0.1 mm 14.73.4 56.8 24.8 ¹⁾Cocoalkyl sulfate sodium salt, 35% by weight activesubstance ²⁾Lauryl sulfate sodium salt, 35% by weight active substance

Examples 6 to 8 show that, for the same water content of the endproduct, the throughput of paste was increased from 8.5 to 13.5 kg/hwhen the powder was recycled. The quantity recycled can be varied withinwide limits (Examples 7 and 8). The product of Example 8 is much coarserthan the product of Example 1. Examples 9 and 10 show that an increasein throughput without any recycling of powder can lead to an increase inthe water content of the product from 0.7 to 1.3% by weight. Recyclingof the powder (Example 11) reduced product moisture and again led topowders with a smaller dust content.

What is claimed is:
 1. A process for producing solid detergent granulescomprising simultaneously drying and granulating an aqueous surfactantpaste comprising an anionic surfactant, an amphoteric surfactant ormixtures thereof in the presence of at least one of (a) from 0.05 to 1%by weight of an alkali metal carbonate, and (b) an alkaline gas stream,in a horizontal thin-layer evaporator or dryer having rotating fittings,wherein the drying is carried out at a temperature of from 120° C. to130° C. and at atmospheric pressure.
 2. The process of claim 1 whereinthe surfactant is selected from the group consisting of soaps, alkylbenzenesulfonates, alkane sulfonates, olefin sulfonates, alkyl ethersulfonates, glycerol ether sulfonates, alpha-methyl ester sulfonates,sulfofatty acids, alkyl sulfates, alkenyl sulfates, alkyl ethersulfates, alkenyl ether sulfates, glycerol ether sulfates, hydroxy mixedether sulfates, monoglyceride sulfates, monoglyceride ether sulfates,fatty acid amide sulfates, fatty acid amide ethersulfates, mono- anddialkyl sulfosuccinates, mono- and dialkyl sulfosuccinamates,sulfotriglycerides, amide soaps, ether carboxylic acids and saltsthereof, fatty acid isethionates, fatty acid sarcosinates, fatty acidtaurides, N-acyl amino acids, alkyl oligoglucoside sulfates, proteinfatty acid condensates, alkyl phosphates, alkyl etherphosphates, alkylbetaines, alkyl amidobetaines, aminopropionates, aminoglycinates,imidazolinium betaines and sulfobetaines.
 3. The process of claim 2wherein the alkyl or alkenyl sulfate corresponds to formula (I):R¹O—SO₃X  (I) wherein R¹ is a linear or branched, aliphatic alkyl oralkenyl group containing 6 to 22 carbon atoms and X is an alkali metal,alkaline earth metal, ammonium, alkylammonium, alkanolammonium orglucammonium.
 4. The process of claim 3 wherein R¹ is a linear orbranched, aliphatic alkyl or alkenyl group containing 12 to 18 carbonatoms.
 5. The process of claim 2 wherein the alkyl ether sulfatecorresponds to formula (II): R²O—(CH₂CH₂O)_(m)SO₃X  (II) wherein R² is alinear or branched alkyl or alkenyl group containing 6 to 22 carbonatoms, m is a number of 1 to 10 and X is an alkali metal, alkaline earthmetal, ammonium, alkylammonium, alkanolammonium or glucammonium.
 6. Theprocess of claim 2 wherein the sulfosuccinate corresponds to formula(III):

wherein R³ is an alkyl or alkenyl group containing 6 to 22 carbon atoms,R⁴ has the same meaning as R³ or X, p and q independently of one anotherstand for 0 or for numbers of from 1 to 10 and X is an alkali metal,alkaline earth metal, ammonium, alkylammonium, alkanolammonium orglucammonium.
 7. The process of claim 2 wherein the betaine correspondsto formula (IV):

wherein R⁵ represents alkyl or alkenyl groups containing 6 to 22 carbonatoms, R⁶ represents hydrogen or alkyl groups containing 1 to 4 carbonatoms, R⁷ represents an alkyl group containing 1 to 4 carbon atoms, x isa number of 1 to 6 and Y is an alkali metal, alkaline earth metal orammonium.
 8. The process of claim 2 wherein the betaine corresponds toformula (V):

wherein R⁸CO is an aliphatic acyl group containing 6 to 22 carbon atomsand 0 to 3 double bonds, y is a number of 1 to 3, R⁶ represents hydrogenor alkyl groups containing 1 to 4 carbon atoms, R⁷ represents an alkylgroup containing 1 to 4 carbon atoms, x is a number of 1 to 6 and Y isan alkali metal, alkaline earth metal or ammonium.
 9. The process ofclaim 1 comprising removal of water by a gas stream.
 10. The process ofclaim 9 wherein said gas stream comprises an alkaline gas stream. 11.The process of claim 1 wherein the alkali metal carbonate is present inthe aqueous paste.
 12. The process of claim 1 wherein the soliddetergent granules have a bulk density of greater than 600 grams perliter.
 13. The process of claim 1 wherein the aqueous surfactant pastecomprises 5 to 80 percent by weight of active substance.
 14. The processof claim 13 wherein the aqueous surfactant paste comprises 10 to 70percent by weight of active substance.
 15. The process of claim 1wherein the aqueous surfactant paste comprises at least 30 percent byweight of solids.
 16. The process of claim 15 wherein the aqueoussurfactant paste comprises at least 50 percent by weight of solids. 17.The process of claim 16 wherein the aqueous surfactant paste comprisesup to 70 percent by weight of solids.
 18. The process of claim 1 whereinthe aqueous surfactant paste further comprises an alkyl or alkenyloligoglycoside nonionic surfactant, or mixtures thereof.
 19. The processof claim 18 wherein the ratio of anionic and amphoteric surfactant toalkyl and alkenyl oligoglycoside is from 10:90 to 90:10 by weight basedon the active substance.
 20. The process of claim 19 wherein the ratioof anionic and amphoteric surfactant to alkyl and alkenyl oligoglycosideis from 25:75 to 75:25 by weight based on the active substance.
 21. Theprocess of claim 18 wherein the aqueous surfactant paste comprises asulfosuccinate and an alkyl olioglucoside in the ratio of 40:60 to 60:40by weight based on the active substance.
 22. The process of claim 1further comprising heating the aqueous paste to 40° C. to 60° C. priorto introduction into the dryer or evaporator.
 23. The process of claim 1further comprising back-mixing dried end-product with the aqueoussurfactant paste prior to drying and granulation.
 24. The process ofclaim 23 comprising back-mixing with said aqueous surfactant paste from10 to 40 percent by weight of dried end-product based on the mass of theaqueous surfactant paste.
 25. The process of claim 24 comprisingback-mixing with said aqueous surfactant paste from 15 to 25 percent byweight of dried end-product based on the mass of the aqueous surfactantpaste.
 26. The process of claim 1 further comprising transferring thedry solid detergent granules to a conveyor belt, wherein the temperatureof said solid detergent granules is from 50° C. to 70° C., and rapidlycooling said granules to temperatures of 30° C. to 40° C. using ambientair.
 27. The process of claim 26 wherein the solid detergent granulesare cooled from 50° C. to 70° C. down to 30° C. to 40° C. in 20 to 60seconds.
 28. A process for producing solid detergent granules comprisingthe steps of A) introducing an aqueous paste comprising an anionicsurfactant, an amphoteric surfactant, or mixtures thereof into ahorizontal thin-layer evaporator or dryer having rotating fittings; B)simultaneously drying and granulating the aqueous paste at a temperaturein the range of 120 to 130° C. in the presence of at least one of (a)from 0.05 to 0.5% by weight of an alkali metal carbonate, and (b) analkaline gas stream, wherein the drying process is carried out atatmospheric pressure and water is removed by a stream of gas; and C)removing the resulting dry solid detergent granules from the evaporatoror dryer.
 29. The process of claim 28 wherein the aqueous paste isheated to a temperature of from 40 to 60° C. prior to step A).
 30. Theprocess of claim 28 wherein following step B) the resulting dry soliddetergent granules at a temperature of 50 to 70° C. are transferred to aconveyor belt and rapidly cooled to a temperature of 30 to 40° C. usingambient air.
 31. The process of claim 28 wherein from 10 to 40% byweight of the resulting dry solid detergent granules removed in step C)are reintroduced into the horizontal thin-layer evaporator or dryer. 32.The process of claim 31 wherein said percentage is from 15 to 25% byweight.
 33. The process of claim 28 wherein in step B) an alkaline gasstream is employed.